This application claims the priority of Korean Patent Application No. 2002-9097, filed on Feb. 20, 2002 and Korean Patent Application No. 2001-19568, filed Apr. 12, 2001, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an actuator of an optical pickup used to record information on and/or to reproduce information from a disc, and more particularly, to an optical pickup actuator that compensates for deflection error caused by curvature of a disc, an optical pickup employing the optical pickup actuator, and an optical recording/reproducing apparatus employing the optical pickup.
2. Description of the Related Art
In general, optical pickups are embedded in optical recording/reproducing apparatuses to record information on and/or to reproduce information from optical recording media, such as discs. Optical pickups record and/or reproduce information by radiating a light beam onto a recording surface of a disc and receiving a light beam reflected back from the recording surface while moving radially around the disc.
FIGS. 1 through 3 are views of an optical pickup actuator included in an optical pickup. The optical pickup actuator includes a base 7, a holder 8 fixed on the base 7, a bobbin 2 moveably supported by elastic supports 6 having one end fixed to the holder 8 and on which an objective lens 1 is mounted, a focusing coil 3 and tracking coils 4, respectively, mounted on the bobbin 2 so as to form paths through which currents flow to drive the objective lens 1 in a focusing direction A and/or a tracking direction B, and a magnet 10 which generates a magnetic field that interacts with respective currents flowing through the focusing coil 3 and tracking coils 4 to produce an electromagnetic force used to drive the bobbin 2, and a yoke 9.
The optical pickup actuator having the above-mentioned structure is disposed opposite to a disc D, and moves radially around the disc D, recording information on and/or reproducing information from the disc D. Reference numerals 11 and 12 denote a turntable on which the disc D is seated, and a motor to turn the turntable, respectively.
In the above-mentioned structure, if a current is supplied to the focusing coil 3, the bobbin 2 is driven in the focusing direction A by an electromagnetic force generated by an interaction of the supplied current and the magnetic field of the magnet 10. In this case, a vertical focusing direction is determined according to a direction of the current supplied to the focusing coil 3. Thus, a focal distance between the recording surface of the disc D and the objective lens 1 is controllable by adjusting an amount of the current flowing through the focusing coil 3. In a similar way, the bobbin 2 is drivable in the tracking direction B by an electromagnetic force generated by an interaction of a supplied current and the magnetic field of the magnet 10. By controlling an amount of current flowing through the tracking coils 4 the objective lens 1 is enabled to accurately follow a desired track on the disc D.
The recording surface of the disc D should be formed to be level. However, the disc D is usually slightly curved upward or downward. The curvature of the disc D creates a kind of focusing error when the disc D is operated with the optical pickup actuator. In particular, when the disc D exhibiting the curvature rotates on the turntable 11, the focal distance between the objective lens 1 of the optical pickup actuator and the disc D varies by an amount corresponding to a displacement of the disc surface from a flat plane due to the curvature thereof. To compensate for a variation due to the curvature of the disc, the optical pickup actuator performs a focus control.
Further, since the bobbin 2 moves in an arc by hanging on one end of the elastic supports 6, due to an error in a manufacturing process or a problem with the structure of the optical pickup actuator, the bobbin 2 does not accurately move in either of a vertical direction or horizontal direction during respective focusing and tracking operations. Instead, the bobbin 2 exhibits a rolling phenomenon in which the bobbin 2 tilts to one side or tilts either backward or forward. The rolling phenomenon includes a tangential direction rolling in which the bobbin 2 tilts about an axis parallel to the a radius vector of the disc D at a position of the bobbin 2, as shown in FIG. 2, and a radial direction rolling in which the bobbin 2 tilts about an axis parallel to the tangent of the disc D at a position of the bobbin 2, as shown in FIG. 3. Tilting of the bobbin 2 toward a center of the disc D is referred to as (+) rolling, and tilting of the bobbin 2 toward an outer perimeter of the disk D is referred to as (xe2x88x92) rolling.
It is an aspect of the present invention to provide an optical pickup actuator which can control rolling in a radial direction so as to compensate for curvature of a disc during a focusing operation, an optical pickup employing the optical pickup actuator, and an optical recording/reproducing apparatus employing the optical pickup.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and or other aspects, there is provided an optical pickup actuator. The actuator includes a base having a holder, a bobbin mounting an objective lens, a plurality of elastic supports having one end coupled to the holder and another end coupled to the bobbin such that the bobbin is movably supported, and a magnetic driving portion which drives the bobbin in a focusing direction and/or a tracking direction. The plurality of elastic supports comprises inner elastic supports that are positioned on a side of the optical pickup actuator closest to a center of a disc and outer elastic supports that are positioned on an opposite side of the optical pickup actuator closest to an outer perimeter of the disc, and the inner elastic supports and outer elastic supports have different lengths.
The outer elastic supports are longer than the inner elastic supports.
The difference in a length between the outer elastic supports and the inner elastic supports is greater than 0 and less than 3 mm.
To achieve the above and/or other aspects, there is provided an optical pickup including an optical system having an objective lens and a optical pickup actuator, the pickup actuator being provided to control focusing and tracking servos of the objective lens to record information on and/or to reproduce information from a disc. The optical pickup actuator includes a base having a holder, a bobbin mounting the objective lens, a plurality of elastic supports having one end coupled to the holder and another end coupled to the bobbin such that the bobbin is movably supported, the plurality of elastic supports including inner elastic supports that are positioned on a side of the optical pickup actuator closest to center of the disc and outer elastic supports that are positioned on an opposite side of the optical pickup actuator closest to an outer perimeter of the disc, the inner elastic supports and outer elastic supports having different lengths, and a magnetic driving portion which drives the bobbin in a focusing direction and/or a tracking direction.
To achieve the above and/or other aspects, there is provided an optical recording/reproducing apparatus comprising a spindle motor which rotates a disc, an optical pickup which is movably disposed in a radial direction of the disc by a pickup actuator, a driving portion which drives the spindle motor and the optical pickup, and a controlling portion which controls focusing and tracking servos of the optical pickup. The pickup actuator includes a base having a holder, a bobbin mounting an objective lens, a plurality of elastic supports having one end coupled to the holder and another end coupled to the bobbin such that the bobbin is movably supported, the plurality of elastic supports including inner elastic supports that are positioned on a side of the optical pickup actuator closest to a center of the disc and outer elastic supports that are positioned on an opposite side of the pickup actuator closest to an outer perimeter of the disc, the inner elastic supports and outer elastic supports having different lengths, and a magnetic driving portion which drives the bobbin in a focusing direction and/or a tracking direction.